Electrosurgical device having floating-potential electrode and curvilinear profile

ABSTRACT

Disclosed herein are embodiments of an electrosurgical device that include one or more floating electrodes and are specifically adapted to remove, cut, resect, ablate, vaporize, denaturize, drill, coagulate and form lesions in soft tissues, with or without externally supplied liquids, preferably in combination with a resectoscope, particularly in the context of urological, gynecological, laparoscopic, arthroscopic, and ENT procedures. Specific adaptations for urological and gynecological applications, for example kidney stone removal and BPH treatment, are also described.

PRIORITY

This application is a divisional of U.S. patent application Ser. No.13/451,138 filed Apr. 19, 2012, which, in turn, is a divisional of U.S.patent application Ser. No. 11/859,297 filed Sep. 21, 2007, now U.S.Pat. No. 8,177,784, issued May 15, 2012, which, in turn, claims thebenefit of U.S. Provisional Application No. 60/847,496 filed Sep. 27,2006, the entire contents of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly, to high efficiency electrosurgical devices andmethods which use radio frequency (RF) energy to cut, resect, ablate,vaporize, denaturize, drill, coagulate and form lesions in soft tissues,with or without externally supplied liquids. The electrosurgical devicesof the instant invention find particular utility in combination with aresectoscope, in the context of urological, gynecological, laparoscopic,arthroscopic, and ENT procedures.

BACKGROUND OF THE INVENTION

As compared to conventional tissue removal techniques, electrosurgicalprocedures are advantageous in that they generally reduce patientbleeding and trauma. More recently, electrosurgical devices have gainedsignificant popularity due to their ability to accomplish outcomes withreduced patient pain and accelerated return of the patient to normalactivities. Such instruments are electrically energized, typically usingan RF generator operating at a frequency between 100 kHz to over 4 MHz.

Many types of electrosurgical devices are currently in use. They can bedivided to two general categories—monopolar devices and bipolar devices.When monopolar electrosurgical devices are used, the RF currentgenerally flows from an exposed active electrode, through the patient'sbody, to a passive, return current electrode that is externally attachedto a suitable location on the patient body. In this manner, thepatient's body becomes part of the return current circuit. In thecontext of bipolar electrosurgical devices, both the active and thereturn current electrodes are exposed, and are typically positioned inclose proximity to each other, preferably mounted on the sameinstrument. In bipolar procedures, the RF current flows from the activeelectrode to the return electrode through the nearby tissue andconductive fluids.

High frequency electrosurgical instruments, both monopolar and bipolar,have been used in the context of many surgical procedures in such fieldsas urology, gynecology, laparoscopy, general surgery, arthroscopy, earnose and throat and more. In many fields of electrosurgery, monopolarand bipolar instruments operate according to the same principles. Forexample, the electrosurgical interventional instrument, whethermonopolar or bipolar, may be introduced through a cannula, aresectoscope, or alternatively directly to perform the needed surgicalprocedure in the target area of the patient's body. In some cases, anexternally supplied liquid (often referred to as an “irrigant”), eitherelectrically conductive or non-conductive, is applied. In otherelectrosurgical procedures, the instruments rely only on locallyavailable bodily fluids, without requiring an external source of fluid.Procedures performed in this manner are often referred to as performedin “dry-field”. When necessary, the electrosurgical instruments may beequipped with irrigation, aspiration or both.

Even though the benefits are well recognized, current electrosurgicalinstruments and procedures suffer from very significant deficiencies.For example, monopolar devices require the use of an additional externalcomponent, namely one or more grounding plates, remotely attached to asuitable location on the skin of the patient. Thus, in that monopolardevices require current to flow from the active electrode through thepatient's body, they invariably allow for the possibility that some ofthe current will flow through undefined paths in the patient's body,particularly when the instrument is not properly designed andpositioned.

Bipolar electrosurgical devices have their own inherent drawbacks, oftenresulting from the close orientation of the return and activeelectrodes. The return electrode necessarily has a small area and, as aresult, can cause undesired tissue heating, coagulating or evaporationat its contact point with the patient's tissue due to the relativelyhigh current densities present thereon. In addition, with the bipolarconfiguration, the close proximity of the active and return electrodescreates the danger that the current will short across the electrodes.For this reason, bipolar devices normally operate at relatively lowvoltage (typically 100 to 500 V) to decrease the chances that a sparkwill bridge the gap between the active and return electrodes.

Electrosurgical procedures which cut or vaporize tissue rely ongeneration of sparks in the vicinity of the active electrodes tovaporize the tissue. Sparking is often referred to as “arcing” withingaseous bubbles in liquid, or alternatively as plasmas. Operation atrelatively low voltage, as is necessary with bipolar instruments, leadsto less efficient sparking, reduced efficiency of the instrument,undesirable overheating of nearby tissue, and longer procedure time.Moreover, the use of electrosurgical bipolar procedures in electricallyconductive environments is inherently problematic. For example, manyarthroscopic procedures require flushing of the region to be treatedwith saline, both to maintain an isotonic environment, to carry awayprocess heat and debris, and to keep the field of view clear. Thepresence of saline, which is a highly conductive electrolyte, can alsocause electrical shorting of a bipolar electrosurgical probe, therebycausing probe destruction and unintended and unnecessary heating in thetreatment environment which, in turn, can result in unintended anduncontrolled tissue destruction.

In addition, current monopolar and bipolar instruments used to cut orvaporize tissue often do not have effective means for controllingbubbles, which is essential to the safety and efficiency of manyprocedures. As a result, the efficiency of the instruments is often lowand the procedure length is increased. Electrosurgical instruments thatlack an effective means for trapping of bubbles include, for example,cutting loops, rollers, needles and knives, resection instruments andablators. Furthermore, many current monopolar and bipolar instrumentsare not designed to take full advantage of either the electricalproperties of the fluids present in the vicinity of the procedure site(bodily fluids, including blood, as well as irrigation fluids, eitherelectrically conductive or non-conductive) or the electrical propertiesof the tissue itself.

Vaporizing electrodes (ablators) currently available for use inconductive liquids, whether monopolar or bipolar, have an activeelectrode surrounded by an insulator that is significantly larger insize than the ablating surface of the electrode. For ablators with acircular geometry, the diameter of the portion of the probe whichgenerates ablative arcs (i.e., the “working” diameter) is generally notgreater than 70 to 80 percent of the diameter of the insulator (i.e.,the “physical” diameter). Accordingly, only about 50% of the physicalprobe area can be considered effective. This increases the size of thedistal end of the electrode necessary to achieve a given ablativesurface size, and necessitates the use of cannulae, often withunnecessarily large lumens, an undesirable condition.

As noted above, it is well known in the prior art to use high frequencycurrent in electrosurgical instruments, both monopolar and bipolar,introduced via a cannula, resectoscope, endoscope or directly, toperform the desired surgical procedure in such fields as urology,gynecology, laparoscopy, general surgery, arthroscopy, ear nose andthroat and more. In fact, a number of radio frequency devices, bothmonopolar and bipolar, and techniques, both in conductive andnon-conductive fluids, are described in the art for urological andgynecological purposes. Illustrative examples include: Alschibaja et al.[(2006) BJU Int. 97(2):243-6]; Botto [(2001) J. of Endourology, 15 (3)313-316]; and Keoghane (pinpointmedical.com/urology) as well as U.S.Pat. Nos. 3,856,015 (Iglesias), 3,901,242 (Storz), and 2,448,741 (Scottet al.), which illustrate prior art cutting electrode assemblies forurology, gynecology and endoscopy. Other examples include: Smith (U.S.Pat. No. 5,195,959) and Pao (U.S. Pat. No. 4,674,499), which describemonopolar and bipolar electrosurgical devices, respectively, thatinclude irrigation channels. Finally, Eggers et al. (U.S. Pat. No.6,113,597) describes bipolar instruments for resecting and/or ablatingtissue within the urethra, prostate and bladder.

Endoscopic transurethral resection and/or thermal treatment of tissue isgenerally accomplished using a resectoscope, a device which allows thescope and other instruments to pass easily into the urethra.Resectoscopes are well known in the art. For example, in U.S. Pat. No.4,726,370, Karasawa et al. describe a conventional resectoscope deviceand electrodes suited for use therewith. Various elongated probes areused to cut, vaporize, coagulate, or otherwise thermally treat tissue.Additional electrosurgical probes for use with a resectoscope aredisclosed by Grossi et al. in U.S. Pat. Nos. 4,917,082, 6,033,400, and6,197,025. Resectoscopes, along with their associated electrosurgicalprobes, are also used in various laparoscopic and gynecologicalprocedures.

Endoscopic electrosurgical probes of the type used with a resectoscopemay be used with conductive or nonconductive irrigants. When conductiveirrigants are used, current flows and/or arcing from any uninsulatedportion of the active electrode which contacts the conductive fluid. Dueto this reality, probes for use in conductive fluids must be insulatedexcept for portions which will give the desired clinical effect duringuse. In a nonconductive fluid environment, conduction occurs only fromportions of the active electrode which are in sufficiently closeproximity to tissue to cause current flows and/or arcing between theelectrode and the tissue, or from portions of the electrode which are incontact with tissue. During a surgical procedure, however, evennon-conductive irrigants can achieve some level of conductivity, forexample as a result of bodily fluids seeping from the patient's tissueinto the irrigant. This contamination may increase the localconductivity to a degree sufficient to cause significant current flowfrom uninsulated portions of a probe designed for use in anon-conductive irrigant. Accordingly, it may be presumed that all fluidshave some level of conductivity during laparoscopic electrosurgery, andthat all probes which are used partially or completely submerged in aliquid will benefit from a construction that maximizes electrodeefficiency by maximizing the portion of the RF energy which providesclinical benefit.

Probes may be used for vaporization or for thermal modification, such aslesion formation. Vaporization occurs when the current density at theactive electrode is sufficient to cause localized boiling of the fluidat the active electrode, and arcing within the bubbles formed. When thecurrent density is insufficient to cause boiling, the tissue inproximity to the active electrode is exposed to high-temperature liquidand high current density. The temperature of the liquid and tissue isaffected by the current density at the active electrode, and the flow offluid in proximity to the electrode. The current density is determinedby the probe design and by the power applied to the probe. Any givenprobe, therefore, can function as either a vaporizing probe or a thermaltreatment probe, depending on the choice of the power applied to theprobe. Lower powers will cause a probe to operate in a thermal treatmentmode rather than in the vaporizing mode possible if higher power isapplied.

The bubbles which form at the active electrode when a probe is used invaporizing mode, form first in regions of the highest current densityand lowest convection of the liquid. When they reach a critical size,these bubbles support arcing within and allow for vaporization oftissue. Bubbles also form in areas of lower current density as theconductive liquid in these regions reaches sufficient temperature. Whilethese bubbles generally do not support arcing, they cover portions ofthe exposed electrode surface, thereby insulating these portions of thesurface. This insulation of non-productive regions of the electrodedecreases non-beneficial current flow into the liquid thereby allowingthe electrode to achieve its clinically beneficial results at lowerpower levels. It is possible to increase electrode efficiency bymanaging these bubbles so as to retain them in regions in which theirpresence insulates the electrode.

In summary, the geometry, shape and materials used for the design andconstruction of electrosurgical instruments greatly affect theperformance. Electrodes with inefficient designs will requiresubstantially higher power levels than those with efficient designs.While currently available electrodes are capable of achieving desiredsurgical effects, they are not efficient for accomplishing these tasksand may result in undesired side effects to the patient.

SUMMARY OF THE INVENTION

In view of the everpresent need in the art for more efficient electrodedesign, it is accordingly an object of the present invention to providean electrosurgical device which has high efficiency.

It is also an object of the present invention to provide anelectrosurgical device which may be readily used in combination with aresectoscope

It is further an object of the present invention to provide anelectrosurgical device which may be used in applications in which thetarget tissue is not submerged in a liquid environment.

It is additionally an object of the present invention to provide anelectrosurgical device capable of operating in electrically conductiveand non-conductive fluid environments, as well as in dry fields (bodilyfluids).

These and other objects are accomplished in the invention hereindisclosed, which is directed to an advanced, high efficiency,electrosurgical device designed for use with a resectoscope, andequipped with one or more additional metallic electrodes which are notconnected directly to any part of power supply circuit. Thisdisconnected electrode may contact the surrounding conducting liquidand/or tissue. The electrical potential of this disconnected electrodeis “floating” and is determined by the size and position of theelectrode, the tissue type and properties, and the presence or absenceof bodily fluids or externally supplied fluid. “Floating” electrodes forelectrosurgery are described in co-pending U.S. patent application Ser.Nos. 10/911,309 (published as US 2005-0065510) and 11/136,514 (publishedas US 2005-023446), the contents of which are incorporated by referenceherein in their entirety. In the context of the present invention, the“floating” electrode is preferably mounted in such a way that oneportion of the electrode is in close proximity to the tip of the activeelectrode, in the region of high potential. Another portion of thefloating electrode is preferably placed farther away, in a region ofotherwise low potential. This region of low potential may be in contactwith the fluid environment, in contact with tissue, or both.

In the context of the present invention, the floating electrodegenerates and concentrates high power density in the vicinity of theactive region, and results in more efficient liquid heating, steambubble formation and bubble trapping in this region. This increases theprobe efficiency, which, in turn, allows the surgeon to substantiallydecrease the applied RF power and thereby reduce the likelihood ofpatient burns and unintended local tissue injury. The probe may beoperated so that the portion of the floating electrode in closeproximity to the active electrode has sufficient current density toproduce vaporization of the liquid and arcing so as to vaporize tissue.Alternatively, the probe may be operated so that the floating electrodecontacts tissue, wherein those portions of the floating electrode incontact with the tissue have sufficient current density to thermallycoagulate blood vessels and tissue. This is particularly useful forachieving hemostasis in vascular tissue, such as, for instance, thatpresent when performing tonsillectomies.

The innovative electrosurgical devices with floating electrodes of thepresent invention may be very effective in other medical procedures,other than those involving tissue evaporation (ablation), including, forinstance, for thermal tissue treatment, lesion formation, tissuesculpting, tissue “drilling”, and coagulation with or without externallysupplied liquids.

Accordingly, in view of these noted needs and objectives, the presentinvention provides in one embodiment an electrosurgical instrumentcomprising:

-   -   (a) an elongate shaft having a proximal end configured for        connection to an electrosurgical power source and a distal end        having an electrode assembly mounted thereto;    -   (b) a conductive member coupled to the elongate shaft and        extending between the proximal and distal ends thereof; and    -   (c) an electrode assembly having an active surface that forms an        acute angle with the longitudinal axis of the shaft and        comprises conductive active and floating electrodes positioned        in close proximity to each other and separated by a        non-conductive dielectric insulator;    -   wherein the active surface includes a continuous or        discontinuous array of raised and recessed portions that creates        regions of high current density for high efficiency vaporization        of tissue.

In another preferred embodiment, the present invention provides anelectrosurgical instrument as described above, with the exception thatthe electrode assembly has a layered construction (referred to as asandwich construction) comprised of (i) an active electrode having upperand lower surfaces; (ii) an insulator having upper and lower surfaces,wherein the upper surface of the insulator is adhered to the lowersurface of the active electrode; and (iii) a floating electrode havingupper and lower surfaces, wherein the upper surface of the floatingelectrode adhered to the lower surface of the insulator.

In a further preferred embodiment, the present invention provides anelectrosurgical instrument as described above, with the exception thatthe electrode assembly comprises an active electrode, a floatingelectrode, and an insulator separating the active and floatingelectrodes, wherein the insulator is concentrically disposed about theactive electrode, and the floating electrode is concentrically disposedabout the insulator;

In the context of the present invention, the electrosurgical deviceherein disclosed may take the form of a probe for use with aresectoscope, wherein the probe has an elongated proximal portion and anactive distal portion, the distal portion having at its distal end atleast one active electrode and at least one floating electrode. Theactive electrode is preferably connected via cabling disposed within theelongated proximal portion to an externally disposed electrosurgicalgenerator. At least a portion of the distal-most portion of at least onefloating electrode should be positioned in close proximity to at leastone active electrode. In a preferred embodiment, the active electrodehas an ablating surface (often referred to herein as the “activesurface” or “working surface”) composed of an array of raised andrecessed regions particularly configured to maximize bubble retentionand concentrate power density. The array may take the form of, forexample, a plurality of walls and grooves, a plurality of elevated pins,a plurality of bumps and pockets, or a combination thereof. So long asthe array performs the desired function (e.g., bubble retention, powerdensity concentration), the specific design, geometry, arrangement andconfiguration of the array or its components is not particularlylimited. For example, the array be continuous or discontinuous, evenlyor unevenly spaced, composed of raises and recesses that are linear ornon-linear (e.g., curvilinear, wavy, zigzagged, angled, etc.), parallelor circumferential positioned, or the like. In one particularlypreferred embodiment, the array is composed of a plurality of groovesetched into the ablating surface of the active electrode, such groovesbeing of a depth and width for maximal retention of bubbles within thegrooves.

The floating electrode preferably surrounds the active electrode and isseparated therefrom by a dielectric member. The floating electrodeintensifies the electric field in proximity to the active electrode andaids bubble retention when the probe is used to vaporize tissue. Inother embodiments, the probe has irrigation supplied to the probe tip.In still other embodiments, the active electrode has a plurality ofprotuberances formed on its ablating surface. These electrodes may beused for vaporizing tissue by applying sufficient voltage for bubbleformation and arcing, or may be used for thermal treatment of tissue byapplying lower voltages.

Other embodiments include small-diameter, elongated active electrodeshaving distal ends forming spherical radii, cylindrical radii, conicalpoints or other shapes.

In another embodiment, the device may be configured exclusively forthermal treatment by providing an active electrode with a hemisphericalshape.

In still other embodiments, a shaped wire electrode may be used toresect rather than vaporize tissue from a body. In this manner, theelectrode functions as a cutting instrument. An illustrative embodimentof such an electrosurgical instrument may comprise:

-   -   (a) an elongate shaft having a proximal end configured for        connection to an electrosurgical power source and a distal end        having an electrode assembly mounted thereto;    -   (b) a conductive member coupled to the elongate shaft and        extending between the proximal and distal ends thereof;    -   (c) first and second laterally opposed, distally extending,        insulated conductive members mounted to the distal end of the        shaft;    -   (d) a pair of floating electrodes, one concentrically disposed        about the distal end of the first conductive member and the        other concentrically disposed about the distal end of the second        of conductive member;    -   (e) a bubble trap mounted to the distal ends of the first and        second conductive members; and    -   (f) an active loop electrode mounted to the bubble trap,        extending between the first and second conductive members;        -   wherein the bubble trap is formed from a nonconductive            dielectric material while the active loop and floating            electrodes are formed from an electrically conductive            material;        -   further wherein the at least one active electrode is            electrically connected to the conductive member while the at            least one floating electrode is not connected to either the            conductive member or the electrosurgical power source.

In another embodiment, the device may be configured for the treatment ofkidney stones.

The present invention also provides electrosurgical methods whichutilize radio frequency (RF) energy to cut, resect, ablate, vaporize,denaturize, drill, coagulate and form lesions in soft tissues, with orwithout externally supplied liquids, for example, in the context ofurological, gynecological, laparoscopic, arthroscopic, and ENTprocedures. In an illustrative embodiment, the present inventionprovides a method of treating benign prostatic hyperplasia (BPH) in asubject in need thereof, comprising the steps of:

-   -   (a) inserting a resectoscope outer sheath into the urethra of a        subject;    -   (b) advancing the resectoscope outer sheath until the distal end        is adjacent a target site of the prostate of the subject;    -   (c) advancing a resectoscope working element with telescope and        an electrosurgical instrument of the present invention through        the resectoscope outer sheath to the target site;    -   (d) introducing an irrigant to the target site so as to submerge        the active and floating electrodes of the electrosurgical        instrument; and    -   (e) applying current to the active electrode of the        electrosurgical instrument and moving the electrosurgical        instrument in a proximal direction relative to the prostate        tissue;    -   wherein step (e) results in vaporization, thermal modification        and hemostatic dessication of adjacent prostate tissue.

These and other objects and features of the invention will become morefully apparent when the following detailed description is read inconjunction with the accompanying figures and examples. However, it isto be understood that both the foregoing summary of the invention andthe following detailed description are of a preferred embodiment, andnot restrictive of the invention or other alternate embodiments of theinvention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of an electrosurgical probe constructed inaccordance with the principles of this invention.

FIG. 2 is an expanded plan view of the distal portion of the object ofFIG. 1.

FIG. 3 is a side elevational view of the objects of FIG. 2.

FIG. 4 is a bottom side plan view of the objects of FIG. 2.

FIG. 5 is an expanded perspective view of the distal portion of theobjects of FIG. 1.

FIG. 6 is an expanded distal axial view of the objects of FIG. 1.

FIG. 7 is an expanded bottom side plan view of the distal-most portionof the objects of FIG. 2.

FIG. 8 is a side elevational sectional view of the objects of FIG. 5.

FIG. 9 is a side elevational sectional view of the objects of FIG. 5during use.

FIG. 10 is a side elevational sectional view of the distal-most portionof an alternate embodiment.

FIG. 11 is a perspective view of another alternate embodiment.

FIG. 12 is a plan view of the objects of FIG. 11.

FIG. 13 is a side elevational view of the objects of FIG. 11.

FIG. 14 is a bottom side plan view of the objects of FIG. 11.

FIG. 15 is a plan view of an alternate embodiment.

FIG. 16 is a side elevational view of the objects of FIG. 15.

FIG. 17 is a bottom side plan view of the objects of FIG. 15.

FIG. 18 is an expanded side elevational sectional view of thedistal-most portion of the objects of FIG. 15.

FIG. 19 is a plan view of another alternate embodiment.

FIG. 20 is a side elevational view of the objects of FIG. 19.

FIG. 21 is an expanded side elevational sectional view of thedistal-most portion of the objects of FIG. 19.

FIG. 22 is a perspective view of another alternate embodiment.

FIG. 23 is a perspective view of yet another alternate embodiment.

FIG. 24 is a expanded plan view of the distalmost portion of the objectsof FIG. 23.

FIG. 25 is a side elevational view of the objects of FIG. 24.

FIG. 26 is a bottom side plan view of the objects of FIG. 24.

FIG. 27 is a plan view of the distal portion of an alternate embodiment.

FIG. 28 is a side elevational view of the objects of FIG. 27.

FIG. 29 is an expanded distal end view of the objects of FIG. 27.

FIG. 30 is a perspective view of the objects of FIG. 27

FIG. 31 is a side elevational sectional view of the objects of FIG. 27at location A-A of FIG. 27.

FIG. 32 is a side elevational sectional view of the objects of FIG. 27in use.

FIG. 33 is a perspective view of the distal portion of an alternateembodiment.

FIG. 34 is a plan view of the distal portion of an alternate embodiment.

FIG. 35 is a side elevational view of the objects of FIG. 34.

FIG. 36 is an expanded distal end view of the objects of FIG. 34.

FIG. 37 is a perspective view of the distal portion of an alternateembodiment for ablating kidney stones.

FIG. 38 is a plan view of the objects of FIG. 37.

FIG. 39 is an expanded side elevational sectional view of the objects ofFIG. 37 at location A-A of FIG. 38.

FIG. 40 is an expanded side elevational sectional view of the objects ofFIG. 37 during use.

FIG. 41 is a plan view of the distal portion of an alternate embodimentfor removal of kidney stones.

FIG. 42 is a side elevational sectional view of the objects of FIG. 41at location A-A of location 41.

FIG. 43 is an expanded side sectional elevational view of themid-portion of the objects of FIG. 41 as depicted in FIG. 42.

FIG. 44 is a perspective view of the objects of FIG. 41.

FIG. 45 is an expanded distal end view of the objects of FIG. 41.

FIG. 46 is a side elevational sectional view of the objects of FIG. 41during use.

FIG. 47 is a plan view of an alternate embodiment having aspiration.

FIG. 48 is a side elevational view of the objects of FIG. 47.

FIG. 49 is an expanded axial end view of the objects of FIG. 47.

FIG. 50 a is a plan view of the distal end electrode assembly of analternate embodiment with simplified construction. FIG. 50 b isalternate view of embodiment depicted in FIG. 50 a, with optional returnelectrodes (1280) included.

FIG. 51 a is a side elevational view of the objects of FIG. 50 a. FIG.51 b is alternate view of embodiment depicted in FIG. 51 a, withoptional return electrode (1280) included.

FIG. 52 is a distal axial view of the objects of FIG. 50 a.

FIG. 53 is a perspective view of the objects of FIG. 50 a.

FIG. 54 is a proximal axial view of the objects of FIG. 50 a.

FIG. 55 is an exploded view of the objects of FIG. 50 a.

FIG. 56 is a sectional elevational side view of the probe of FIG. 50 aduring use.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the context of the present invention, the following definitionsapply:

The words “a”, “an”, and “the” as used herein mean “at least one” unlessotherwise specifically indicated.

In common terminology and as used herein, the term “electrode” may referto one or more components of an electrosurgical device (such as anactive electrode or a return electrode) or to the entire device, as inan “ablator electrode” or “cutting electrode”. Such electrosurgicaldevices are often interchangeably referred to herein as “probes” or“instruments”.

The term “proximal” refers to that end or portion which is situatedclosest to the user; in other words, the proximal end of theelectrosurgical device of the instant invention will typically comprisethe handle portion.

The term “distal” refers to that end or portion situated farthest awayfrom the user; in other words, the distal end of the electrosurgicaldevice of the instant invention will typically comprise the activeelectrode portion.

The instant invention has both human medical and veterinaryapplications. Accordingly, the terms “subject” and “patient” are usedinterchangeably herein to refer to the person or animal being treated orexamined. Exemplary animals include house pets, farm animals, and zooanimals. In a preferred embodiment, the subject is a mammal.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. In case of conflict, thepresent specification, including definitions, will control.

As noted above, the present invention is directed to high efficiencymonopolar or bipolar electrosurgical devices and methods which utilizeradio frequency (RF) energy to cut, resect, ablate, vaporize,denaturize, drill, coagulate and form lesions in soft tissues, with orwithout externally supplied liquids, having particular utility in thecontext of urological, gynecological, laparoscopic, arthroscopic, andENT procedures. At its most basic, the device of the present inventionis comprised of electrosurgical probe having a metallic electrode coatedentirely with dielectric, with the exception of an exposed portionlocated at the electrode tip. This exposed tip is referred to herein asthe “active element” or “active electrode” of the probe. When placedinto conductive liquid-tissue media and energized, the probe induceselectrical current in the conducting liquid and nearby tissue. Thiscurrent deposits energy into the liquid and tissue, thereby raising thelocal temperature and creating the desired clinical effect. The highestenergy deposition occurs in areas closely proximate to the active tipwhere current density is largest.

Power density in close proximity to the tip depends primarily on theapplied power, the shape and size of the exposed portion of theelectrode, the surrounding liquid/tissue electrical conductivity as wellas the presence of bubbles. In the sparking regime, the power densityalso depends on the spark distribution and conductivity (i.e., theplasma conductivity). It is further affected by the size, shape, andposition of the return current electrode. In most cases, positioning thereturn electrode in closer proximity to the active electrode increasesthe power density in the region near the electrode tip.

In the case of a monopolar probe, the return current is collected by alarge return electrode (sometimes called dispersive electrode or returnpad) placed on the patient's body, remote from the probe tip. The powerconcentration capability of a monopolar probe is determined by the shapeof the exposed electrode: the smaller and sharper the tip is, the betterits power concentration capability.

In the case of bipolar probes, the return current electrode is placed inmoderate proximity to the active electrode (generally from 1 to 10 mm).In comparison with a monopolar probe having an active electrode ofapproximately the same shape, some additional power concentration takesplace. The power concentration capability can be further controlled bythe shape and position of the return electrode. Decreasing the distancebetween the return electrode and the active electrode increases thepower concentration. A problem arises when the probe is generatingsparks. (Recall that this is the goal of probe operation inablation-tissue evaporation or cutting, for example). If the returnelectrode is placed sufficiently close to the tip to achieve asubstantial increase of power concentration, the breakdown (arcingwithin bubbles) takes place between the tip and return electrode. Thespark conductive channel connects the active electrode to the returncurrent electrode and the power supply is loaded directly by the spark.Usually this leads to an extra high-energy deposition in the sparkbetween metallic electrodes, thereby resulting in localized melting andvaporization of the electrodes themselves. In turn, this results inshorting of the power supply and destruction of both the active andreturn electrodes with little clinical benefit to the patient.

A good bipolar probe design must therefore avoid arcing between theactive and return electrodes. Usually this is achieved by placing thereturn electrode a sufficiently large distance away from the activeelectrode to prevent direct breakdown between electrodes. Nevertheless,periodic arcing may take place such that both electrodes are eroded andeventually destroyed, especially in an aggressive mode of operation.Therefore, the additional degree of power concentration achievable bybipolar probes is severely limited.

In contrast, the electrosurgical device of the present invention has oneor more additional metallic electrodes which are not connected directlyto any part of the power supply circuit, and therefore are called“floating”. These floating electrodes are in contact with the tissueand/or liquid in proximity to the active electrode. The electricalpotential of these additional electrodes is not fixed, but rather is“floating” and is determined by size and position of the electrode andthe electrical conductivity of the tissue and/or liquid surrounding thedistal end of the device. This electrode is positioned in such a waythat one end of the electrode is in close proximity to the activeelectrode. Another portion of the floating electrode is positioned in aregion of low potential in the liquid and/or tissue. The addition ofthis floating electrode thereby substantially modifies the electricalfield distribution, and energy deposition, in the vicinity of the activeelectrode without the possibility of electrode destruction since thefloating electrode is not directly connected to the electrical powersupply.

The floating electrode therefore serves to concentrate the electricfield in the region of the active electrode, but it does not provide acurrent path back to the RF generator that powers the electrosurgicaldevice. In monopolar electrosurgical devices, there is an additionaldispersive return electrode that is in contact with a remote portion ofthe patient's body and is coupled to the RF generator in order tocomplete the return path. In bipolar electrosurgical devices, there is areturn electrode mounted near the active electrode near the distal endof the device, and this return electrode is coupled to the RF generatorin order to complete the return path to ground. In either configuration,a floating electrode may be used to shape the electric field near theactive electrode; however, the floating electrode should not be confusedwith the return electrode, as the floating electrode has no connectionto the RF generator and is, in fact, isolated from the electricalcircuit of the device.

In the absence of sparking (arcing within bubbles), the “floating”electrode increases power density in the vicinity of the probe tip. Thisis because the floating electrode extends from a high potential region(near the active electrode), to a region with low potential (fartherfrom the active electrode), and “shorts” these points together. Theprobe's floating will be between the potentials of these points. Thepresence of the electrode decreases the potential near the activeelectrode, and thereby increases the electric field, current and powerdensity in the region near the active electrode. A floating electrodeworks about the same way as any extended conductive object in anelectrostatic field. The higher power density results in more efficientliquid heating and steam bubble formation, which, in turn, allows one todecrease the power applied to probe for a given effect. In the presenceof the “floating” electrode, more sparks are generated in the activeregion, since this region is larger. Bubble trapping (the retention ofbubbles in selected areas to insulate these areas for improved ablatorefficiency) is greatly enhanced with proper design of the floatingelectrode, insulator and the active electrode.

Sparks are an active element of the electrosurgical process. A spark isgenerated in a steam bubble if the electrical field in the bubble(voltage difference across a bubble) is sufficient for breakdown.Usually sparks are generated in bubbles that are close to the activeelectrode of the probe because current density and field intensity arelargest in this region.

The breakdown or spark inside a bubble is an electrically conductivechannel of partly ionized pressurized gas. This medium is called highlycollisional plasma. The basic property of this plasma is that theconductivity is proportional to the plasma density. Higher plasmatemperatures are associated with higher ionization rates, plasmadensities and conductivity.

Usually energy is deposited into highly collisional plasmas by electriccurrent driven by voltage applied to electrodes at the ends of a plasmachannel. In the case of a plasma channel formed inside of a bubble, theinner parts of the bubble surface having the largest voltage differenceact as the “electrodes” to which the channel is connected. Morefrequently, but not always, one of these electrodes is a metallicsurface of the active electrode and the other is the opposite surface ofthe bubble or the surface of the tissue.

Electrically, the plasma channel is characterized by its impedance. Theefficiency of energy deposition strongly depends on the ratio betweenthe plasma channel and the power supply impedance. Efficiency (theportion of applied energy deposited to the plasma) as high as 50% can beachieved for matched conditions in which the power supply impedanceequals the spark (plasma channel) impedance. If the channel impedance istoo large or too small, the power deposition in the plasma is decreased.

As described previously herein, the additional “floating” electrode cansignificantly increase the energy density in the region surrounding theactive electrode. This makes it possible to substantially increase thepower deposited into the spark. Since the floating electrode can beplaced very close to the probe tip, the largest probability is forbreakdown and plasma channel formation in the region between the twoelectrodes—the active electrode and the floating electrode. The plasmachannel current can now be supported not by a bubble size fraction ofthe induced current, but by a much larger volume of current flow that isdetermined by the size of floating electrode. This floating electrodeadditionally concentrates current delivered to the spark. The optimumspark current can be controlled by adjusting the size and position ofthe floating electrode. Arcing, then, can occur through bubbles betweenthe active and floating electrodes, or from either electrode throughbubbles in contact with that electrode.

In summary, the present invention provides an advanced, electrosurgicalprobe equipped with one or more “floating electrodes” coupled with oneor more active electrode uniquely designed and configured for thermaltissue treatment, including tissue ablation and vaporization, preferablyin combination with a resectoscope. The floating electrode concentratesthe power (i.e., increases the power density) in the active region,which leads to more efficient liquid heating, steam bubble formation,and spark generation in this region. Arcing occurs from the floatingelectrode as well as the active electrode, thereby resulting in a probein which the distal tip has a “working” area equal to the “physical”area. This is in contrast to other prior art probes used in electricallyconductive liquids which generally have an electrically active area thatis significantly smaller than the physical area of the device.

The floating electrode favorably affects bubble formation and trapping,and therefore enhances the probe's performance. This results in highefficiency operation, allowing the surgeon to substantially decrease theapplied RF power and thereby reduce the likelihood of patient burns andinjury, while at the same time maintaining high performance operation.

The method of the present invention includes the step of positioning theelectrosurgical probe adjacent to target tissue at a surgical site sothat at least one of the active electrodes and at least a portion of atleast one of the floating electrodes are in close proximity to thetarget tissue. Conductive or non-conductive irrigant may be supplied tothe probe distal tip in the region between the active electrode(s) andthe target tissue, and between the portion of the floating electrode inclose proximity to the tissue, and the target tissue itself. Otherportions of the floating electrode(s) may be in contact with targettissue, adjacent tissue, or fluid environment. Vacuum may be suppliedvia means within the elongated distal portion to the probe distal tip soas to remove excess irrigant as well as ablation products. The probe isenergized producing high current density and arcing in portions of theactive electrode and floating electrode in close proximity to the targettissue. Lower density current flow from regions of the floatingelectrode(s) in contact with adjacent target tissue results indesiccation of the adjacent tissue so as to achieve hemostasis. Whileenergized, the probe may be moved across the target tissue with abrushing or sweeping motion, or intermittently energized for a briefperiod of time and repositioned so as to affect the target tissue. Whenused with a resectoscope, the probe may be extended axially, energizedand retracted proximally so as to cut a groove in the tissue. Theprocess may be repeated until the desired volume of tissue is removed.The movement of the probe relative to the tissue may be manuallyachieved or alternatively automated, for example, according to theprinciples outlined in U.S. Pat. No. 6,921,398 or U.S. PatentPublication No. 2003-0065321, the contents of which are incorporated byreference herein in their entirety.

The current invention is also useful for medical procedures in whichtissue is thermally treated rather than removed by vaporization, suchas, for instance, cardiology, oncology and treatment of tumors, aprocess sometimes referred to as lesion formation for coagulation and/ordenaturing of tissue. In these applications, the device is brought intoclose proximity, or contact, with tissue with or without the presence ofexternally applied irrigant at the site for thermal treatment. Thevoltage applied to the active electrode is reduced to a level whichproduces current densities insufficient for forming sparks and theassociated bubbles. Tissue is heated to a desired temperature for apredetermined time sufficient for lesion formation. The floatingelectrode intensifies the electric field in the region surrounding theactive electrode so as to produce a larger, more controlled and moreuniform lesion.

EXAMPLES

Hereinafter, the present invention is described in more detail byreference to the exemplary embodiments. However, the following examplesonly illustrate aspects of the invention and in no way are intended tolimit the scope of the present invention. As such, embodiments similaror equivalent to those described herein can be used in the practice ortesting of the present invention.

Referring to FIGS. 1 through 4, which depict an electrosurgical probespecifically configured for use with a resectosope (not shown) andconstructed in accordance with the principles of this invention, probe100 has an elongated tubular member 102 with a proximal end 104 havingan electrical connector 106 suitable for connecting via an electricalcable to an electrosurgical generator, and a distal end 108. Members 110have proximal ends 112 mounted to distal end 108 of elongated tubularmember 102, and distal ends 114 to which are mounted electrode assembly116. Optional electrode stabilizer 118 for stabilizing the distal end ofprobe 100 is intended to be proximately disposed to a distal region of atelescope mounted in a resectoscope working element. However, it isenvisioned that stabilizer 118 is not required to practice thisinvention. Conductive member 120 covered by insulation 122 extends fromelectrical connector 106 to proximal end 124 of insulated conductivemember 126.

Referring now to FIGS. 5-8, which depict the distal-most portion ofprobe 100, referred to herein as the active head, electrode assembly 116includes active electrode 130, insulator 132 and floating electrode 134.Active electrode 130 has a plurality of grooves 136 of width 138 anddepth 140, width 138 and depth 140 being selected to trap bubbles in thegrooves. However, as noted previously, the present invention is notlimited to the grooved design depicted but encompasses any activeelectrode ablating surface specifically configured to maximize bubbleretention and concentrate power density. So long as the ablating surfaceperforms the desired function (e.g., bubble retention, power densityconcentration), the specific design, geometry, arrangement andconfiguration of the array or its components is not particularlylimited. Accordingly, the ablating surface may be composed of an arrayof raised and recessed regions, e.g., a plurality of walls and grooves,a plurality of elevated pins, a plurality of bumps and pockets, or acombination thereof. As noted previously, the array be continuous ordiscontinuous, evenly or unevenly spaced, composed of raises andrecesses that are linear or non-linear (e.g., curvilinear, wavy,zigzagged, angled, etc.), parallel or circumferential positioned, or thelike.

Active electrode 130 and floating electrode 134 are preferably formedfrom a suitable metallic material, examples of which include, but arenot limited to, stainless steel, nickel, titanium, tungsten, and thelike. Insulator 132 is preferably formed from a suitable dielectricmaterial, example of which include, but are not limited to, alumina,zirconia, and high-temperature polymers. As shown in FIG. 8, activeelectrode 130 preferably protrudes beyond insulator 132 a distance 142.In turn, insulator 132 preferably protrudes beyond floating electrode134 a distance 144. Insulated conductive member 126 has a conductiveportion 146 coated with dielectric material 148. Distal end 150 portion146 is connected to active electrode 130. Active electrode 130 hassurface 152 segmented by grooves 136. Surface 136 forms an acute angle154 with the axis of tubular member 102. Angle 154 is preferably between0 and 90 degrees, more preferably between 5 and 80 degrees, morepreferably between 10 and 70 degrees, more preferably between 15 and 60degrees, even more preferably between 20 and 50 degrees.

Referring now to FIG. 9, which depicts a probe 100 in use in aconductive liquid environment, probe 100 is moved axially in direction160 relative to the tissue which is connected to a return electrode at aremote location. Current (depicted by arrows 162) flows from conductor126 to active electrode 130, and then from active electrode 130 throughthe conductive fluid to the tissue and the return electrode. A portionof the current flows through the floating electrode, the currententering the portion of the floating electrode in the high-potentialportion of the electric field in close proximity to the activeelectrode, and exiting in portions of the floating electrode inlow-potential regions farther removed from the active electrode. Currentflowing through the conductive liquid heats the liquid, the heating at alocation being proportional to the current density at that location.Where the current density is sufficient, the conductive liquid boils,forming steam bubbles. Some of the bubbles 164 are trapped in grooves136 where their presence decreases current flow from the surfaces of thegroove, thereby effectively insulating the groove. Other bubbles form atsurface 152. When these bubbles reach a sufficient size, arcing 166occurs within some of these bubbles, the resistance to arcing being lessthan the resistance of the alternate path for current flow around thebubble. In some cases, the bubbles at surface 152 intersect portions oftissue that are in close proximity. When arcing occurs within thesebubbles, the arc is between active electrode 130 and the tissue, and inthis manner a portion of the tissue is vaporized. Current density at theportions of the floating electrode in high-potential portion of theelectric field, in close proximity to the active electrode, also may besufficient to cause boiling of the liquid, bubble formation, arcingwithin bubbles, and arcing between the floating electrode and tissue soas to vaporize tissue.

The active or ablating surface 152 of active electrode 130 of probe 100is preferably planar. However, in some circumstances, it may beadvantageous to have surface 152 take other, non-planar forms. Forexample, in an alternate embodiment shown in FIG. 10, active surface 152of probe 200 is curved, preferably in a cylindrical manner having aradius 160. In other embodiments, surface 152 may have other curvilinearprofiles. In still other embodiments, surface 152 may have a non-uniformcross-section and take the shape of, for example, a convex sphericalsegment or a concave spherical segment.

Probe 100 is intended for use at a surgical site which is submerged inliquid environment or in which the region surrounding the distal end ofthe probe is irrigated with a irrigant. Probe 300, shown in FIGS. 11through 14, is identical in construction to probe 100, and additionallyhas a means for providing irrigant to a surgical site, particularly theregion surrounding the distal portion of the probe. Tubular member 302is connected via means within tubular member 102 to an external irrigantsource. Flow 304 from distal end 306 of member 302 causes puddling ofirrigant in the region surrounding electrode assembly 116 and tissue incontact with it.

FIGS. 15 through 18 depict an alternate embodiment, including an activeelectrode configured for thermal treatment or vaporization of tissue ina fluid environment. Probe 400, the distal portion of which is depictedin FIGS. 15 through 18, is constructed a fashion analogous to that ofprobe 100, with the exception of electrode assembly 116. Activeelectrode 430 forms an array of cylindrical pins 431 which protrudethrough holes in insulator portion 432, which with insulator portion 433electrically isolate active electrode 430. Insulator portion 432protrudes from floating electrode 434 distance 444. Axial surfaces 452of pins 431 are coplanar and form an acute angle 454 with the axis oftubular portion 102 (FIG. 1). In this context, the acute angle may rangebetween 0 and 90 degrees, more preferably between 5 and 80 degrees, morepreferably between 10 and 70 degrees, more preferably between 15 and 60degrees, even more preferably between 20 and 50 degrees.

It is frequently desirable to precisely vaporize or thermally treatsmall regions of tissue. The embodiment shown in FIGS. 19 through 21 hasan active electrode that forms a hemispherical portion of radius 504.Probe 500 is analogous in construction to probe 100, including anelongated tubular portion 102 with a proximal end electrical connector106 connected by means within portion 102 to the active electrode, and ascope support 118. Active electrode 502 forms a hemisphere of radius504. Insulator 506 is mounted to distal end 104 of tubular portion 102.Tubular floating electrode 508 is mounted to insulator 506. Whenenergized in a conductive fluid environment, floating electrode 508intensifies the field in close proximity to active electrode 502. Distalend 510 of floating electrode 508 is in a high potential region of thefield. Proximal end 512 of floating electrode 508 is in a lowerpotential portion of the field such that current flows through floatingelectrode 508 from distal end 510 to lower potential portions. Thiscurrent flow increases the field intensity thereby increasing theefficiency of the probe. This, in turn, allows procedures to beperformed with less power or more quickly.

A further embodiment, intended for cutting, vaporizing or thermallytreating tissue, is depicted in FIG. 22. Probe 600 is constructed likeprobe 500 except that active electrode 602 forms an elongated portion603 protruding from distal surface 607 of insulator 606. Elongatedportion 603 has a distal end 605 forming a spherical portion 609. Inother embodiments, portion 603 may be cylindrical throughout its entirelength. In still other embodiments, distal end 605 forms a conicalpoint. Floating electrode 608 functions in the same manner as with probe500. That is, floating electrode 608 intensifies the electric field soas to increase the efficiency of probe 600 when vaporizing or thermallytreating tissue.

Another embodiment, the distal portion of which is depicted in FIGS. 23through 26, uses bubble trapping and a floating electrode toaggressively vaporize tissue. Probe 700 is analogous in construction toprobes 500 and 600, comprised of an insulator 706 mounted to distal end108 of tubular portion 102, a tubular floating electrode 708 mounted toinsulator 706, and an active electrode 702 protruding from the distalportion of insulator 706. Active electrode 702 has a distal-most surface715 inclined at angle 717 to axis 713. Angle 717 preferably rangesbetween 0 and 90 degrees, more preferably ranges between 5 and 60degrees, more preferably between 10 and 55 degrees, even more preferablybetween 30 and 50. Distal-most surfaces 709 of floating electrode 708and 711 of insulator 706 are approximately parallel to distal-mostsurface 715 of active electrode 702. Grooves 721 are of a depth andwidth suitable for trapping bubbles as taught in the description ofprobe 100.

Cutting loop electrodes are well known in the art. For example, Grossiet al, in U.S. Pat. No. 4,917,082, describes a resectoscope electrodethat utilizes a formed wire cutting loop as the active electrode. Theelectrode, intended for use in non-conductive liquids, has insulatingtubes (elements 51 and 53 of Grossi FIG. 2) which cover inner sleeves(elements 50 and 52 of Grossi FIG. 2) but cover no portion of thecutting loop (element 48 of Grossi FIG. 2). This is typical of probesdesigned for use with non-conductive irrigants since, if the irrigant isideally non-conductive, current flows only from those portions of theuninsulated portions which are in contact with or sufficiently closeproximity to tissue. If such a probe is placed in a conductive fluidenvironment, current flows from all uninsulated surfaces, both those ofthe formed wire electrode and uninsulated portions of the conductivemembers. A large portion of the power applied to the probe would flowinto the fluid so as to heat the fluid with no clinical benefit. Thispower loss would necessitate the use of high power levels to achieve thedesired cutting action.

FIGS. 27 through 31 depict a cutting loop electrode configured for usein a liquid environment and constructed in accordance with theprinciples of this invention. Probe 800, the distal portions of whichare shown in the figures, has a pair of laterally opposed, distallyextending, insulated conductive members 802 having proximal ends 804assembled to distal end 108 of tubular member 102. Conductive members802 are connected via conductive member 120 to proximal end connector106 (FIG. 1). Distal ends 806 of members 802 have mounted thereto formedelectrode 808. Bubble trap 810, made from a suitable dielectricmaterial, is mounted to upper portions 812 of electrode 808. As bestseen in FIG. 31, members 802 have a conductive inner portion 814, aninsulating coating 816 which covers distal ends 806, upper portion 812of electrode 808, and portion 811 of bubble trap 810. Tubular floatingelectrodes 820 are mounted to members 802 adjacent to distal ends 806 ofmembers 802.

Referring now to FIG. 32 which depicts loop electrode 800 in use,electrode 800 is moved in a proximal direction 830 relative to tissue atthe surgical site such that electrode 808 removes a portion of tissue832. Where electrode 808 is in contact with tissue, current 801 flowsfrom active electrode 808 into the tissue, the high current densitypresent causing vaporization of tissue so as to allow portion 832 to beseparated from the remaining tissue. Current also flows from portions ofelectrode 808 which are uninsulated and in contact with the liquidenvironment, the current density being sufficient to cause boiling ofthe fluid adjacent to the wire, and arcing within some of the bubbles.The arcing begins when a bubble reaches a critical size, and stops whenthe bubble reaches a size which will no longer support arcing. Bubbleswhich are too large to support arcing may remain in contact with theactive electrode due to surface tension, such bubbles thereby insulatingthe portion of the electrode surface to which they adhere. The buoyancyof the bubbles, and natural convection currents resulting from theheating of the water, act on the bubbles causing them to dislodge fromthe electrode surface. Conductive flow along the surface of electrode808 must flow around bubble trap 810, the deflection of the flow causinga region to form beneath bottom surface of bubble trap 810 which isshielded from the convective flow. Bubbles are retained against surfaceby surface tension, and by the buoyancy of the bubbles. Bubbles beneaththese bubbles tend to remain in the region because of surface tension,shielding from convection currents, and buoyancy of the bubbles. Thepresence of the bubbles, particularly large bubbles, partially insulatesthe portions of electrode 808 above the tissue so as to reduce currentflow from these portions thereby increasing the efficiency of probe 800.

During use, current (represented by arrows 801) flows from 808 activeelectrode to the tissue or to the liquid environment. A portion of thecurrent flows through floating electrode 820, entering distal portionwhich is in a high-potential portion of the electric field formed byactive electrode 808, and leaving from floating electrode 820 in moreproximal portions which are in lower potential portions of the electricfield. The current then flows to the return which may be a dispersivepad, or a return electrode located on the instrument. As with otherembodiments, the current flow through the floating electrodes increasesthe current density in the portions of the field around the floatingelectrodes. This increased current density increases current flow at theactive electrode thereby increasing the electrode efficiency.

Other configurations of the bubble trap and floating electrode arecontemplated in the present invention. For instance, FIG. 33 shows analternate embodiment in which bubble traps 810 are circular membersattached to upper portions 812 (see FIG. 31) of electrode 808. Bubbletraps 810 function in the same manner as those of the embodimentdepicted in FIGS. 27 through 32. In other embodiments, bubble traps 810have other shapes such as, for instance, elliptical, oblong, or anirregular shape when viewed in plan view as in FIG. 27. In otherembodiments, surface 811 may be non-planar, for example concave, or withraised edges so as to better retain bubbles in contact with surface 811.FIGS. 34 through 36 depict an alternate embodiment in which floatingelectrode 820 is a planar plate mounted to the upper surface of bubbletrap 810. Lateral portions 819 of floating electrode 820 in closeproximity to active electrode 808 are in high-potential regions of theelectric field. Medial portion 821 of floating electrode 820 is in alower potential region of the electric field. Current flow in thefloating electrode is from the high-potential regions in close proximityto active electrode 808 to medial regions in lower potential regions.This current flow, as with previous embodiments, increases currentdensity in region of the active electrode thereby increasing theinstrument efficiency.

Yet another disclosed embodiment may be used to reduce the size ofkidney stones so that they can be aspirated from the patient. Referringto FIGS. 37 through 39 which depict the distal portion of an ablatorprobe for eroding kidney stones, probe 900 has a tubular activeelectrode 902 which is assembled to tubular member 904 such that activeelectrode 902 is electrically connected to proximal electrical connector106 (FIG. 1). Tubular member 904 and proximal end 906 of ceramicinsulator 908 are covered by dielectric coating 910. Floating electrode912 is mounted to distal portion 914 of insulator 908. Floatingelectrode 912 has a cylindrical proximal portion 916, and a flareddistal portion 918 protruding beyond active electrode 902 by a distance920. Lumen 922 of active electrode 902 and lumen 924 of tubular member904 together form an aspiration path between the distal opening 926 ofactive electrode 902 and an external vacuum source. In a preferredembodiment, the external vacuum source has a means for controlling thevacuum level.

Referring now to FIG. 40, depicting probe 900 in use eroding a kidneystone 990, a slight vacuum applied to opening 926 of active electrode902 draws conductive liquid down the aspiration path and holds stone 990in contact with or close proximity to the distal end of probe 900.Current (represented by arrows 980) flows from active electrode 902 tothe conductive fluid and therefrom to a return electrode, the returnelectrode being either a dispersive pad (e.g., a monopolar application)or a return electrode on the probe (e.g., a bipolar application). Alarge portion of the current flows through floating electrode 912,entering in the distal portion 918 which is in close proximity to activeelectrode 902, and exiting in the portions of proximal portion 916 whichare in lower potential portions of the electric field. High currentdensity occurs in the conductive liquid in close proximity to bothactive electrode 902 and floating electrode 912. This causes rapidlocalized heating of the fluid, boiling of the fluid, and, when thebubbles formed reach a critical size, arcing within some of the bubbles.Some of the bubbles which intersect the active electrode and the surfaceof the stone, or which intersect the floating electrode and surface ofthe stone, support arcs 992 which affect the surface of the stone,vaporizing material in proximity to the arcs. This vaporization, alongwith fracturing of the stone caused by intense thermal gradients,creates debris which is aspirated from the site via lumen 922 of activeelectrode 902 and lumen 924 of tubular member 904. The process continuesuntil stone 990 is sufficiently eroded for aspiration via probe 900 orother means.

In another embodiment configured for removal of kidney stones, amechanism is provided for grasping a stone, and positioning andretaining it in proximity to the active and floating electrodes.Specifically FIGS. 41 through 45 depict the distal portion of probe 1100having a subassembly 1101 for grasping stones slidably assembledthereto. Subassembly 1101 has a grasping element 1102 and a tubularcontrol element 1103. Grasping element 1102 has a tubular proximalportion 1104 and a distal grasping portion 1106 having arms 1108. Arms1108 have angled distal portions 1110 to aid in grasping a stone, andproximal portions 1112 formed to a radius and attached to the distal endof tubular proximal portion 1104 of element 1102. Tubular controlelement 1103 has at its distal end 1114 internal surface portion 1116 ofradius 1118. Control element 1103 is slidably positioned on graspingelement 1102 such that, when element 1103 is advanced distally relativeto element 1102, surface 1116 acts on proximal portions 1112 of arms1108 so as to deflect arms 1108 inwardly so as to grasp a stone inproximity to the distal end of probe 1100. When a stone has been graspedby arms 1108, subassembly 1101 (elements 1102 and 1103) is movedproximally until the stone is in contact with floating electrode 1120.Active electrode 1122 has a sharpened distal portion 1124 and a proximalportion 1126 which is assembled to conductive tubular member 1128.Insulator 1130 is assembled to active electrode 1122. Tubular member1128 and proximal portion 1132 of insulator 1130 are covered withdielectic coating 1134.

Referring now to FIG. 46, which depicts probe 1100 in use, stone 1140 ispositioned in close proximity to or contact with floating electrode1120. Current (depicted by arrows 1142) flows from active electrode 1122to a return electrode located at a remote location (e.g., a monopolarapplication) or on the instrument (e.g., a bipolar application). Aportion of the current flows from active electrode 1122 to portions offloating electrode 1120 in close proximity to the active electrode, andthen floating electrode 1120 via the surrounding conductive liquid tothe return electrode. A portion of the current flowing to floatingelectrode 1120 flows through stone 1140. A portion of this currentcauses arcing at active electrode 1122 and/or arcing at floatingelectrode 1120, the arcing causing erosion and fracturing of stone 1140.

Aspiration may also be advantageous when vaporizing tissue. Bubblesformed during ablation of tissue may obscure the view of the surgeon andform pockets which displace conductive liquid from the surgical site. Anelectrosurgical probe formed in accordance with the principles of thisinvention and having ablation is depicted in FIGS. 47 through 49. Probe1000 is constructed identically to probe 100 shown in FIGS. 1 through 9,but has added thereto aspiration tube 1002 which is in communicationwith an external vacuum source by means within tubular member 102.Distal end 1004 of tube 1002 is positioned on the back side of electrodeassembly 116 so that liquid aspirated from the site contains only wasteheat, rather than process heat as would be the case if distal end 1004were in close proximity to active electrode 152.

Referring now to FIGS. 50 a through 55, which depict the distal-mostportion of probe 1200, referred to herein as the active head, electrodeassembly 1216 includes active electrode 1230, insulator 1232 andfloating electrode 1234. Active electrode 1230 has a plurality ofgrooves 1236 of width 1238 and depth 1240, width 1238 and depth 1240being selected to trap bubbles in the grooves. Active electrode 1230 andfloating electrode 1234 are preferably formed from a suitable metallicmaterial, examples of which include, but are not limited to, such asstainless steel, nickel, titanium, tungsten, and the like. Insulator1232 is preferably formed from a suitable dielectric material, exampleof which include, but are not limited to, alumina, zirconia, andhigh-temperature polymers. Members 1210, insulated by dielectric coating1211, have affixed to distal ends 1214 of active electrode 1230 suchthat electrical power may be conducted by members 1210 to activeelectrode 1230. Members 1210 are connected by at least one conductivemember of probe 1200 and external cabling to a suitable RF generator.

As with previously described embodiments, current flows from activeelectrode 1230 to the tissue or to the liquid environment, with aportion of the current flowing through floating electrode 1234. Thecurrent then flows to a return which may be a dispersive pad (notshown), or one or more return electrode 1280 located on the probe thatare electrically connected to the electrosurgical generator (not shown).As with other embodiments, the current flow through the floatingelectrodes increases the current density in the portions of the fieldaround the floating electrodes. This increased current density increasescurrent flow at the active electrode thereby increasing the electrodeefficiency.

As best seen in FIG. 55, insulator 1232 has a first portion 1260 whichinsulates top surfaces 1262 of active electrode 1230, and a secondportion 1264 which electrically isolates floating electrode 1234 fromactive electrode 1230. As best seen in FIG. 51, electrode assembly 1216has a beveled lower portion 1266 formed on the lower distal portion ofportion 1264 of insulator 1232 and the lower portion of floatingelectrode 1234. When viewed axially in the distal direction as in FIG.54, floating electrode 1234 and second portion 1264 of insulator 1232are flush with, or recessed behind active electrode 1230. Surface 1236forms an acute angle 1254 with the axis of member 1210. Angle 1254 ispreferably between 0 and 90 degrees, more preferably between 20 and 60degrees.

Electrode assembly 1216 of probe 1200 has a simple construction whichmay be produced at low cost. Active electrode 1230 may be formed bymachining using wire Electrical Discharge Machining and conventionalmachining, or by metal injection molding. Floating electrode 1234 may bestamped at low cost from sheet material. Insulator 1232 may be made bypressing and sintering, or by ceramic injection molding. Activeelectrode 1230 is joined to insulator 1232, and insulator 1232 is joinedto floating electrode 1234 by a suitable biocompatible adhesive such as,for instance, EP62-1 MED or EP3HTMED epoxies by Master Bond Incorporated(Hackensack, N.J.) or Cement 31 by Sauereisen Incorporated (Pittsburgh,Pa.), all of which maintain their adhesive properties at thetemperatures to which assembly 1216 may be heated during use.Alternatively, assembly 1216 may be held together by mechanical means,for example using fasteners such as screws, nuts, rivets or the like.Because members 1210 conduct power to active electrode 1230, it is notnecessary to have a separate conductor such as conductor 126 of probe100 (FIGS. 5 through 8), thereby further reducing the cost of probe1200.

Probe 1200 is particularly useful for treating Benign ProstaticHyperplasia (BPH), commonly referred to enlarged prostate. Surgicaltreatment of this condition is commonly accomplished using aresectoscope in a procedure referred to TransUrethral Resection of theProstate (TURP). The resectoscope outer sheath is inserted into theurethra and the distal end advanced until it is near the prostate. Theresectoscope working element with telescope and RF probe are insertedinto the outer sheath such that the distal end of the probe can be usedto modify or remove tissue. Most commonly, a cutting loop electrode(like that taught by Grossi et al in U.S. Pat. No. 4,917,082) is used tocut strips of tissue from the interior of the prostate, the site beingfilled with non-conductive irrigant. When sufficient tissue has beenremoved, the site including the bladder is flushed with irrigant toremove tissue strips that may remain at the site. The time required toflush the tissue from the site is frequently a significant portion ofthe total procedure time. Additionally, the use of non-conductiveirrigant may lead to TUR syndrome, a potentially serious low bloodsodium level. Gyms ACMI (Southboro, Mass.) has developed bipolar RFdevices which operate in conductive irrigant. One of the productsremoves tissue by bulk vaporization so as to make removal of remainingtissue strips after resection unnecessary. Because the system isbipolar, its efficiency is low. As a result, high power levels arerequired to achieve acceptably high tissue removal rates. As notedpreviously, excessive power levels can lead to unintended injury tolocal tissue. The bipolar products are usable with conductive irrigantsonly.

Probe 1200 may be used to efficiently perform TURP procedures usingeither non-conductive or conductive irrigants. When non-conductiveirrigant is introduced into the body, blood and other highly conductivebodily fluids contaminate the irrigant thereby making it conductive, thelevel of conductivity depending on the degree of contamination. Whenprobe 1200 is submerged in an irrigant with any level of conductivity,floating electrode 1234 intensifies the electric field in closeproximity to active electrode 1230 thereby increasing the currentdensity and making conditions more favorable for tissue vaporization.This allows probe 1200 to be effectively used when either conductive ornon-conductive irrigants are supplied to the site, the selection beingbased on surgeon preference.

Referring to FIG. 56 depicting probe 1200 in the context of a TURPprocedure, probe 1200 is moved in a proximal direction 1278 relative totissue 1279. Current (indicated by arrows 1284) from the RF generator,is supplied to active electrode 1230 by elements 1210. The current 1284then flows from active electrode 1230 to a return electrode andtherefrom to the generator. A portion of the current flows throughtissue 1279 to tissue in close proximity to region 1286 of floatingelectrode 1234 in close proximity to active electrode 1230. This currentflows through floating electrode 1234 to portion 1288 of floatingelectrode 1234 in a lower potential region of the electric field, andfrom floating electrode 1234 to the irrigant and therethrough to thereturn electrode. Some of the current flowing from active electrode 1230to tissue 1279 causes boiling of irrigant in close proximity, arcingwith the bubbles formed, and vaporization of tissue in the mannerpreviously herein described. A portion of the current flow at region1286 of floating electrode 1234 may have sufficient density to causeboiling, arcing and vaporization of tissue. A larger portion of thecurrent flow has insufficient density to causing boiling of theirrigant, but does cause heating of the irrigant to elevatedtemperatures less than 100° C. The heated irrigant in these regions oflower current density causes thermal modification of adjacent tissue,specifically dessication of the tissue resulting in hemostasis.

When using probe 1200 to perform a TURP, a resectoscope sheath isintroduced to the site in the standard manner. The working element withtelescope and probe 1200 is inserted into the resectoscope sheath. Probe1200 is extended distally past the end of the prostate slightly into thebladder. The distal end of the resectoscope is lowered somewhat suchthat when probe 1200 is energized and retracted proximally into theresectoscope, tissue intersected by active electrode assembly 1216 isvaporized so as to form a channel or groove in the prostate tissue. Thescope position is adjusted and the process repeated to remove additionaltissue. The process is repeated until the required volume of tissue isremoved. Current flowing between active electrode 1230 and floatingelectrode 1234 thermally coagulates adjacent tissue thereby producinghemostasis.

All publications, patent applications, patents and other referencesmentioned herein are incorporated by reference in their entirety.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed:
 1. An electrosurgical instrument comprising: a. anelongate conductive shaft having a proximal end configured forconnection to an electrosurgical power source and a distal endconfigured for connection to an electrode assembly; and b. saidelectrode assembly mounted to the distal end of said elongate conductiveshaft that comprises an active electrode and an insulator wherein; i.said insulator is formed from a nonconductive dielectric material,comprises opposed first and second surfaces, and includes a projectionon the opposed second surface that extends away from the opposed secondsurface and at least one hole that passes through said projection andterminates at the opposed first surface, ii. said active electrode isformed from an electrically conductive material and comprises opposedactive and insulated sides connected by a peripheral edge surface,further wherein said active side comprises an exposed curvilinearablating surface and said insulated side is in direct contact with saidopposed first surface of said insulator; c. wherein said elongateconductive shaft extends through said at least one hole and passesthrough said opposed first and second surfaces of said insulator to bein electrical contact with said active electrode; d. further wherein adielectric coating covers said elongate conductive shaft, extending fromsaid elongate conductive shaft proximal end to said electrode assemblyand overlapping at least a portion of said projection.
 2. Theelectrosurgical instrument of claim 1, wherein said exposed curvilinearablating surface comprises a convex spherical segment.
 3. Theelectrosurgical instrument of claim 2, wherein said insulated sidecomprises a planar surface.
 4. The electrosurgical instrument of claim3, wherein said active electrode is electrically connected to saidelongate conductive shaft by means of one or more conductive leads thatextend from the distal end of said elongate conductive shaft and throughsaid planar surface of said insulated side of said active electrode. 5.The electrosurgical instrument of claim 4, wherein said one or moreconductive leads are coated with a dielectric material.
 6. Theelectrosurgical instrument of claim 1, wherein said electrode assemblyfurther comprises at least one floating electrode that is not directlyelectrically connected to either the elongate conductive shaft or theelectrosurgical power source but is in direct physical contact with saidopposed second surface of said insulator such that said insulator isdisposed between said active electrode and said at least one floatingelectrode.
 7. The electrosurgical instrument of claim 6, wherein saidactive and said at least one floating electrode are formed from asuitable metallic material selected from the group consisting ofstainless steel, nickel, titanium, and tungsten whereas the insulator isformed from a suitable dielectric material selected from the groupconsisting of alumina, zirconia, and high-temperature polymers.
 8. Theelectrosurgical instrument of claim 6, wherein said at least onefloating electrode is concentrically disposed about the peripheral edgesurface of said active electrode.
 9. The electrosurgical instrument ofclaim 6, wherein said active electrode, said insulator and said at leastone floating electrode have distal most surfaces, further wherein thedistal most surface of said active electrode protrudes beyond the distalmost, surface of said insulator and the distal most surface of saidinsulator protrudes beyond the distal most surface of said at least onefloating electrode.
 10. The electrosurgical instrument of claim 9,wherein said distal most surfaces of said at least one floatingelectrode, said insulator, and said active electrode are approximatelyparallel.
 11. The electrosurgical instrument of claim 1, furthercomprising at least one lumen disposed along a length of said elongateconductive shaft, said at least one lumen configured to deliver anirrigant to the electrode assembly.
 12. The electrosurgical instrumentof claim 1, further comprising at least one lumen disposed along alength of said elongate conductive shaft, said at least one lumenforming an aspiration path between the active electrode and an externalvacuum source.
 13. The electrosurgical instrument of claim 1, furthercomprising an electrode stabilizer mounted to the distal end of theelongate conductive shaft for stabilizing the electrode assembly. 14.The electrosurgical instrument of claim 1, wherein said electrosurgicalinstrument further comprises a return electrode that is electricallyconnected to said elongate conductive shaft.
 15. The electrosurgicalinstrument of claim 1, wherein said insulator is concentrically disposedabout the peripheral edge surface of said active electrode.
 16. Theelectrosurgical instrument of claim 1, wherein said elongate conductiveshaft comprises a linear proximal portion defining a longitudinal axisand an off-axis distal portion that passes through the opposed first andsecond surfaces of said insulator.